1. Field of the Invention
The instant disclosure relates to a RF power amplifier; in particular, to the RF power amplifier with a quiescent operating current which is stable.
2. Description of Related Art
With the advancement of the internet, people are accustomed to receive information quickly and heavily, especially advancement of wireless communication technology. After personal mobile products, such as mobile phone, personal digital assistant and other products, are popular with an amazing speed, people want to be able to obtain real-time information, but also want to have instant online-support. Therefore, wireless local area network (WLAN) combining internet and wireless communication and third-generation (3G)/fourth generation (4G) network are solutions to meet the demands of people.
Among hand-held wireless communication products, main direct current (DC) power consumption comes from a RF power amplifier. Therefore, to keep a high linearity of the RF power amplifier instead of distorting an amplified signal, and to maintain a high efficiency to support a long time of communication has always been a focus in designing the RF power amplifier. In particular, there is an obvious characteristic of a time-varying wave packet when a broadly used digital modulation technique of orthogonal frequency-division multiplexing (OFDM) is adopted in a wireless communication system, and a constant of peak to average power ratio (PAPR) of which is way higher than that of the current wireless communication system; in other words, the variation of the wave packet with time is more dramatic, and thus a demand of the linearity of the RF power amplifier is higher.
However, in prior art, the RF power amplifier provided by U.S. Patent Publication No. US2003/6556082 does not be affected by ambient temperature, but a quiescent operating current outputted from the RF power amplifier may be affected in the face of the battery voltage. To third-generation (3G)/fourth generation (4G) mobile phone system, for example, 3G/4G mobile phone system has great demand for accuracy of RF output power. Because voltage value of the phone battery may change between 3.2 volt and 4.2 volt, accuracy of RF output power of the RF power amplifier may be affected.